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rcu: define __rcu address space modifier for sparse

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This commit provides definitions for the __rcu annotation defined earlier.
This annotation permits sparse to check for correct use of RCU-protected
pointers.  If a pointer that is annotated with __rcu is accessed
directly (as opposed to via rcu_dereference(), rcu_assign_pointer(),
or one of their variants), sparse can be made to complain.  To enable
such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER
kernel configuration option.  Please note that these sparse complaints are
intended to be a debugging aid, -not- a code-style-enforcement mechanism.

There are special rcu_dereference_protected() and rcu_access_pointer()
accessors for use when RCU read-side protection is not required, for
example, when no other CPU has access to the data structure in question
or while the current CPU hold the update-side lock.

This patch also updates a number of docbook comments that were showing
their age.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christopher Li <sparse@chrisli.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2010-04-28 14:39:09 -07:00
parent d34a16661e
commit ca5ecddfa8
5 changed files with 260 additions and 148 deletions
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27
include/linux/srcu.h
View file

@ -108,12 +108,31 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/**
* srcu_dereference - fetch SRCU-protected pointer with checking
* srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
* @p: the pointer to fetch and protect for later dereferencing
* @sp: pointer to the srcu_struct, which is used to check that we
* really are in an SRCU read-side critical section.
* @c: condition to check for update-side use
*
* Makes rcu_dereference_check() do the dirty work.
* If PROVE_RCU is enabled, invoking this outside of an RCU read-side
* critical section will result in an RCU-lockdep splat, unless @c evaluates
* to 1. The @c argument will normally be a logical expression containing
* lockdep_is_held() calls.
*/
#define srcu_dereference(p, sp) \
rcu_dereference_check(p, srcu_read_lock_held(sp))
#define srcu_dereference_check(p, sp, c) \
__rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
/**
* srcu_dereference - fetch SRCU-protected pointer for later dereferencing
* @p: the pointer to fetch and protect for later dereferencing
* @sp: pointer to the srcu_struct, which is used to check that we
* really are in an SRCU read-side critical section.
*
* Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
* is enabled, invoking this outside of an RCU read-side critical
* section will result in an RCU-lockdep splat.
*/
#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
/**
* srcu_read_lock - register a new reader for an SRCU-protected structure.